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152 rev port estomatol med dent cir maxilofac. 2021;62(3):150-156

the fracture resistance of full -contour crowns milled from 1:1 Standard 1600424 -001, Bien -Air Dental, Bienne, Switzerland).
some of the new resin nanoceramic CAD/CAM blocks; this jus- The dental preparation was digitally scanned (Zirkonzahn
tifies the relevance of this pilot study. S600 ARTI, Zirkonzahn GmbH, Austria) to obtain its three-
The objective of this study was to evaluate the influence -dimensional model. An anatomical crown of a lower second
of the type of cement on the fracture resistance of full -contour premolar was designed using dedicated CAD software (Zirkon-
resin nanoceramic crowns cemented over dental preparations zahn.Modellier, Zirkonzahn GmbH, Austria).
with knife -edge margins. The null hypothesis was as follows: Twenty full -contour crowns with a 0.2 -mm margin thickness
the type of cement does not influence the fracture resistance were milled from resin nanoceramics CAD/CAM blocks (Cer-
™
of full -contour resin nanoceramic crowns cemented over asmart270 , GC Corporation, Tokyo, Japan; Lot 1901101/1902071;
preparations with knife -edge margins. Val: 01/2024) (Figure 2) using a milling unit (Zirkonzahn M5
Heavy Metal, Zirkonzahn GmbH, Austria), as well as a replica of
the dental preparation in a cobalt-chrome alloy (Zirkonzahn
Material and methods Sintermetall, Zirkonzahn GmbH, Austria), which was used for
mechanical testing (Figure 3). The internal surface of each crown
In this pilot study, 20 full -contour resin nanoceramic crowns was sandblasted with 50 -µm aluminum oxide powder (1.5 bar)
were milled from Cerasmart270 CAD/CAM blocks and ran- for 10 seconds at a distance of 10 mm (Basic classic 2945 -2026,
™
domly divided into two experimental groups. This material is Renfert GmbH, Hilzingen, Germany). Before each test, the co-
a high -density composite resin containing a polymeric ma- balt-chrome alloy die was cleaned with a wet compress and
trix with the addition of silica nanoparticles of up to 1 µm (18)
and barium glass (77% by weight).
A dental preparation for a full -contour crown was per-
formed on a lower right second premolar typodont tooth
mounted on a dental anatomical model (ANA -4, Frasaco
®
GmbH , Germany) (Figure 1). Axial guiding grooves were made
1 -mm deep with a round end taper diamond bur (FG G850.010,
Edenta AG. Hauptstrasse, Switzerland). The axial reduction of
1.5 mm was made with a needle diamond bur (FG G859L.016,
Edenta AG. Hauptstrasse, Switzerland) and the occlusal reduc-
tion of 2.0 mm with a football diamond bur (FG G368.023, Eden-
ta AG, Hauptstrasse, Switzerland) while maintaining the tooth
morphology. The 45º -angle bevel of the functional cusp and the
knife -edge margin were also performed with the needle dia-
mond bur. The dental preparation was finished and polished
with an Arkansas stone (Abrasive 025, Edenta AG. Hauptstrasse,
Switzerland) followed by a fine -grain polishing rubber point
(Exa Intrapol 050, Edenta AG. Hauptstrasse, Switzerland) to
smooth the preparation’s surface. The whole procedure was Figure 2. Full -contour crown milled from Cerasmart270™
executed using rotary instruments with constant water cooling resin nanoceramic CAD/CAM blocks (GC Corporation,
Tokyo, Japan).
(Bora LK 1600732 -001, Bien -Air Dental, Bienne, Switzerland; CA

Figure 1. Dental preparation for a full -contour crown with Figure 3. Cobalt -chrome alloy die (Zirkonzahn
a knife -edge margin, buccal view. Sintermetall, Zirkonzahn GMBH, Austria).